Always eager to prove claims made by his illustrious predecessor, Euler set out to prove what he regarded as a generalization of one of Fermat’s conjectures, which became a theorem in 1994 thanks to Andrew Wiles (see "The fifth operation"). The Swiss mathematician stated:
"Just as there are no two cubes whose sum or difference is a cube, it is certain that it is impossible to find three fourth powers whose sum is a fourth power […]. Similarly, it would seem impossible to find four fifth powers whose sum is a fifth power, and likewise for higher powers."
History proved him wrong!

Leonhard Euler (1707–1783).